The invention relates to a method for determining at least one injection parameter of an internal combustion engine and to an internal combustion engine.
Methods and internal combustion engines of the type addressed here are known. German patent DE 103 56 858 B4 discloses a method in which a time profile of an electrical operating variable of an actuator is measured during the injection operation. The measured profile of the electrical operating variable is compared with a stored reference curve, wherein the reference curve represents the time profile of the operating variable in a reference pattern. An injection parameter, in particular a start of injection, is ascertained as a function of the comparison. It is disadvantageous here that the electrical operating variable or its time profile is linked only indirectly to the injection variables, such as, for example, the start of injection and the injected fuel quantity, which are relevant for the operation of the internal combustion engine. Therefore, for example the actual physical start of the injection of fuel into a cylinder of the internal combustion engine deviates frequently from the start of energization of the injector. In particular, the comparison of the measured profile of the electrical operating variable with the stored reference curve requires a comparatively costly and complex procedure in order to ascertain plausible values for the injection parameter.
It is also known to ascertain injection parameters of an internal combustion engine by evaluating pressure profiles in an injection system which have been detected in a time-resolved manner. In this context, there is a direct relationship between the pressure profile and the injection parameters. However, the problem arises here that a measured pressure profile typically has a frequency mixture which comprises, in particular, the delivery frequency of a high pressure pump of the injection system as well as frequencies which result from reactions of the various injectors. It is therefore not readily possible to determine injection parameters such as the start of injection and the injected fuel quantity from the detected pressure profile. The detected pressure profile is typically filtered, which gives rise to a phase offset and to a loss of information, and there is therefore a need to improve the accuracy of such methods.